Parallel correction amplifier

ABSTRACT

There is disclosed a power supply stage, and a method of controlling such, comprising: a means for generating an intermediate supply signal in dependence on a reference signal representing a desired power supply; and a plurality of adjusting means, each adapted to generate an adjusted supply signal tracking the reference signal, in dependence on the generated intermediate supply signal and the reference signal.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The invention is directed to a modulated supply stage comprising aswitched supply and a correction stage for correcting an error in theswitched supply to generate a modulated supply voltage. The invention isparticularly, but not exclusively, concerned with the provision of amodulated supply voltage to an RF amplifier.

2. Description of the Related Art

United Kingdom Patent No. 2398648 describes a particularly advantageousmodulated supply stage comprising a switched supply stage and an errorcorrection stage. The switched supply stage selects one of a pluralityof supply voltages in dependence on a reference signal representing, inthe preferred implementation, a signal to be amplified by an RF (radiofrequency) amplifier. The error correction stage comprises an errorcorrection amplifier and provides an error correction voltage for acorrection of an error in a switched supply voltage, to deliver a moreaccurate supply voltage to the RF amplifier.

The error correction stage is provided to enable fast correction of theswitched supply stage. There is a trade-off between output power andbandwidth. An increase in output power tends to result in a reduction inbandwidth due to increased parasitic elements of the higher powercorrection amplifier and combining components.

Further, when a transformer is advantageously used to combine theswitched supply voltage and the error correction voltage, the increasein transformer size necessary for increased power handling results inincreased leakage inductance and inter-winding capacitance, and aconsequent loss of bandwidth.

It is an aim of the invention to provide an improvement to theadvantageous modulated power supply described in United Kingdom PatentNo. 2398648, and particularly to provide improvements in the errorcorrection stage.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a power supply stagecomprising: a means for generating an intermediate supply signal independence on a reference signal representing a desired power supply;and a plurality of adjusting means, each adapted to generate an adjustedsupply signal tracking the reference signal, in dependence on thegenerated intermediate supply signal and the reference signal.

There may be further provided a current summing means for summing theplurality of generated adjusted supply signals to provide an outputpower supply voltage with higher output current capability. The higheroutput current capability is preferably a current capability which ishigher than the current capability of any individual adjusted supplysignal

The output power supply stage may be provided as a power supply signalto an RF amplifier.

Each adjusted supply signal may be provided as a power supply signal toan RF amplifier stage comprising a corresponding plurality of RFamplifiers, each adjusted supply signal providing a power supply for oneRF amplifier.

The means for generating a supply signal may be adapted to select one ofa plurality of power supply voltages in dependence on the referencesignal.

There may be provided a plurality of combining means for combining thesupply signal with each of a plurality of correction signals in order togenerate the plurality of adjusted supply signals. Each adjusting meansmay include a correction amplifier for generating a correction signal,wherein each correction amplifier receives as an input a signalrepresenting a difference between the reference signal and the sum ofthe adjusted supply signals. Each combining means may comprise atransformer. The supply signal may be connected to a tap of a primarywinding of each transformer, and a respective correction signal isconnected to a tap of a secondary winding of each transformer, anadjusted supply signal being formed on another tap of the secondarywinding of each transformer.

The summing means may comprise a connection between the taps of thetransformers on which the adjusted supply signals are formed.

The intermediate supply signal may be a voltage supply signal and theadjusted supply signal is a voltage supply signal.

In accordance with the invention there is provided a method ofgenerating an output supply signal comprising: generating anintermediate supply signal in dependence on a reference signalrepresenting a desired power supply; and generating a plurality ofadjusted supply signals tracking the reference signal in dependence onthe intermediate supply signal and the reference signal.

The method may further comprising the step of providing the plurality ofadjusted supply voltages as power supply signals to a correspondingplurality of parallel connected amplifiers.

The method may further comprise the step of summing the plurality ofadjusted supply signals to provide an output power supply voltage.

The method may further comprise the step of providing the summedadjusted supply voltages as a power supply signal to an amplifier.

The step of generating an intermediate supply signal may compriseselecting one of a plurality of power supply voltages in dependence onthe reference signal.

The method may further comprise the step of correction signalsrepresenting an error between the reference signal and an output signal,generating a plurality of amplified versions of the reference signal,and combining each amplified version with the intermediate supply signalto generate the plurality of adjusted supply signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings in which:

FIG. 1 illustrates an exemplary modulated power supply stageincorporating a correction stage including parallel correctionamplifiers in accordance with the invention;

FIG. 2 illustrates an example implementation of the correction stage ofFIG. 1 for delivering a power supply voltage using transformercombiners; and

FIG. 3 illustrates an example implementation of the correction stage ofFIG. 1 for delivering power supply voltages to parallel RF amplificationstages

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is now described by way of example with referenceto exemplary embodiments. One skilled in the art will appreciate thatembodiments are described for ease of understanding the invention, andthe invention is not limited to details of any embodiment described. Thescope of the invention is defined by the appended claims.

In the following description where the same reference numerals are usedin different Figures, they denote an element in one Figure whichcorresponds to an element in another Figure.

FIG. 1 illustrates an exemplary embodiment of a modulated power supplyin accordance with the principles of the invention. The exemplaryembodiment is based on the modulated power supply architecture disclosedin United Kingdom Patent No. 2398648. In general the exemplary modulatedpower supply, generally denoted by reference numeral 100, generates acoarse supply voltage from a switched supply stage. A correction stage,including a correction amplifier, provides high bandwidth correction forthe coarse supply voltage, such that the output voltage of the modulatedpower supply is a corrected voltage.

In accordance with the principles of the invention, as will be discussedfurther hereinbelow, the correction amplifier of the correction stage isimplemented as two or more parallel amplifiers. This allows forimprovements in the operation and implementation of the modulated powersupply stage, and also improvements in the operation and implementationof the overall architecture in which the modulated power supply stage isimplemented.

With further reference to FIG. 1, the modulated power supply stage 100includes a difference block 102, a switched supply stage 104 and a scaleblock 150, which in general can be considered a coarse supply stage.

The difference block 102 receives as a first input a reference signalREF on an input line 112. The reference signal REF is representative ofa signal to be amplified by an RF amplifier for which the modulatedpower supply stage is to generate a supply voltage. The reference signalREF may, for example, be a signal representing the envelope of a signalto be amplified by the RF amplifier.

An output of the difference block 102 forms an input to the switchedsupply stage 104. As known in the art, the switched supply stage isadapted to generate at its output a voltage generated from one of aplurality of fixed voltage levels, in dependence on the signal at itsinput. The invention is not, however, limited to the use of a switchedsupply.

The output of the switched supply stage 104 on line 116 is a switchedvoltage supply V_(SW). The switched voltage supply V_(sw) forms an inputto a scale block 150 which scales the signal before providing it as asecond input to the difference block 102. Thus the difference block 102generates an output to the switched supply which represents an errorbetween the (ideal) reference signal and the actual signal at the outputof the switched supply. In dependence on this error signal, the switchedsupply 104 switches the supply signal at its output.

FIG. 1 does not represent a complete implementation of a coarse supplystage, not does it necessarily represent essential elements of a coarsesupply stage. The difference block 102, switched supply stage 104 andscale block 150 are illustrative of an exemplary implementation, asknown in the art, and which may also require the inclusion of additionalfunctional elements. For example, an output filter may be required atthe output of the switched supply stage 104. The invention is notconcerned with the implementation of the coarse supply stage, and oneskilled in the art will understand that alternatives, modifications orenhancements to the illustrated coarse supply stage are possible.

With further reference to FIG. 1, the modulated power supply stage 100further includes a difference block 106, a correction stage 160(described in further detail below), a current combiner stage 178, and ascale block 152, which in general can be considered an error correctionpath.

The difference block 106 receives as a first input a delayed version ofthe reference signal REF, denoted REF_(DELAY), on line 129. The delayedreference signal REF_(DELAY) on line 129 is generated by a delay block131 which receives as its input the reference signal on line 112.

The output of the difference block 106 forms an input to the correctionstage 160, which in accordance with the principles of the inventioncomprises two or more parallel connected correction amplifiers. In theexample illustrated, for clarity and simplicity, two parallel correctionamplifiers are shown. However in general it will be understood by oneskilled in the art that the principles of the invention extend to anynumber of parallel correction amplifiers n.

The high frequency bandwidth of each of the n amplifiers is greater thanthe bandwidth of a single amplifier having n times the power handlingcapabilities.

The exemplary correction stage 160 illustratively comprises a firstcorrection amplifier 162, a second correction amplifier 164, a firstcombiner 170 and a second combiner 172.

Each of the first and second correction amplifiers 162 and 164 receiveas an input the output of the difference block 106. Each of the firstand second correction amplifiers generates an output on lines 166 and168 respectively, which form first inputs to combiners 170 and 172respectively. In general, for n parallel correction amplifiers, there isprovided n combiners. A second input for each of the combiners 170 and172 is provided by the switched voltage supply V_(SW) on line 116. Eachcombiner 170 and 172 thus combines the output of a respective correctionamplifier 170 and 172 with the switched supply voltage V_(SW) to provideidentical corrected supply voltages on output lines 174 and 176 at theoutputs of the combiners 170 and 172. The correction stage 160 thusprovides a plurality of identical corrected switched supply voltages atits outputs. In general, the correction stage 160 provides n correctedswitched supply voltages.

It should be understood that whilst the correction stage generates aplurality of identical corrected supply voltages, this represents anideal scenario. In practice the plurality of corrected supply voltagemay not be identical due to component tolerances or operating conditionsfor example. The corrected supply voltages can therefore be understoodto be substantially identical.

In general, it can be considered that the correction stage provides aplurality of adjusting means each adapted to generate an adjustedselected power supply voltage tracking the reference signal independence on the power supply signal from the switched supply and thereference signal.

In a first embodiment, a combiner stage 178 is provided as shown in FIG.1, which receives as inputs the corrected switched supply voltages onlines 174 and 176. The identical corrected switched supply voltages formrespective inputs to a current combiner 180 of the combiner stage 178.The current combiner 180 combines the corrected switched supply voltagesto provide as an output a high power corrected switched supply voltageV_(OUT) on line 120. In general the combiner stage 178 combines thecurrent from n corrected switched supply voltages to provide a singleoutput voltage with high current capability.

The output voltage V_(OUT) on line 120 is fed back through the scaleblock 152 to provide a second input to the difference block 106. Thusthe correction amplifiers of the correction stage operate to amplify theerror in the output voltage compared with the delayed (ideal) referencesignal.

The provision of two or more parallel amplifiers in the correction stageallows for a higher output power without a high frequency bandwidthpenalty. To produce the same output power with a single correctionamplifier, there would be a high frequency bandwidth penalty.

By the same principle, the provision of two or more parallel amplifiersin the correction stage allows for an extended high frequency bandwidthfor the same power. In general, the benefit may be a mix of increasedbandwidth and power.

Thus, it is possible (i) to increase power without reducing the highfrequency bandwidth, or (ii) increase the high frequency bandwidthwithout reducing power, or (iii) a combination of both.

In a preferred arrangement, the combiners 170 and 172 are implemented astransformers. The invention has particular advantages when the combinersare implemented as transformers. Each transformer may be made smallerand have increased high frequency bandwidth than if a single high powercorrection amplifier were used with a single higher powertransformer-combiner.

An exemplary implementation using transformers for the combiners 170 and172, and showing how in such an implementation the function of thecombiner 180 may be implemented, is described with reference to FIG. 2.

The output of the correction amplifier 162 on line 166 is provided as aninput to a first tap of a first winding of a transformer 202. The secondtap of the first winding of the transformer 202 is connected toelectrical ground. A first tap of a second winding of the transformer202 is connected to the switched supply voltage V_(SW) on line 116. Thesecond tap of the second winding of the transformer 202 is connected tothe output signal line 174. The provision and connection of thetransformer in this way results in the corrected switched supply voltagebeing generated at the second tap of the second winding, and thus online 174.

The output of the correction amplifier 164 on line 168 is provided as aninput to a first tap of a first winding of a transformer 204. The secondtap of the first winding of the transformer 204 is connected toelectrical ground. A first tap of a second winding of the transformer204 is connected to the switched supply voltage V_(SW) on line 116. Thesecond tap of the second winding of the transformer 204 is connected tothe output signal line 176. The provision and connection of thetransformer in this way results in the corrected switched supply voltagebeing generated at the second tap of the second winding, and thus online 176.

In this way the correction stage 160 generates the two identicalcorrected switched supply voltages on lines 174 and 176.

The exemplary combining stage 178 of FIG. 2, which receives thecorrected switched supply voltages, combines the current from thecorrected switched supply voltages by electrically connecting theoutputs of the transformers. Thus it can be seen that the two outputlines are connected together, and the corrected switched supply voltageoutput V_(OUT) is provided on line 120. This principle as illustrated inFIG. 2 extends to n transformers, and the electrical connection of ntransformer outputs to provide an overall output.

For completeness, in FIG. 2, there is illustrated an RF amplifier 210 towhich the modulated supply voltage stage may be arranged to provide asupply voltage. The supply voltage is provided by the corrected switchedsupply voltage on line 120. The RF amplifier, illustratively, amplifiesan input signal on line 212 and provides an amplified output on line214.

Each correction amplifier 162 and 164 (and associated transformerwindings) may be a push-pull arrangement fed from two halves of a supplyrail. However for the purposes of illustration and simplicity, theinvention is described in FIG. 2 on the basis of a single supply rail.

In accordance with the general benefits of the invention as mentionedabove, the arrangement of FIG. 2, where respective transformer outputsignals on lines 174 and 176 are combined to feed a single RF amplifier,allows increased bandwidth for a given power level to be achieved due toreduced parasitic elements (the leakage inductance of the transformerand inter-winding capacitance), since the transformer can be madephysically smaller. Alternatively, it is possible to provide more powerwithout degrading bandwidth. To achieve this, n transformers (driven byn correction amplifiers) of the same size and bandwidth as a singlestage design can be used in parallel to feed a single high-powered RFamplifier.

However, as known in the art, there is a limit as to how much power asingle RF amplifier can handle, because of limitations associated with atransistor on which the RF amplifier is based. For this reason, it isknown in the art of high power amplification to split the RF amplifierinto multiple stages, and provide two or more RF amplifiers in parallel,connected to amplify the same input signal and have their outputscombined. Such a parallel amplifier arrangement can be advantageouslycombined with the present invention.

In a second embodiment, the arrangement of FIGS. 1 and 2 described aboveis modified. This is illustrated with reference to FIG. 3. Only theportions of FIG. 1 necessary to understand the modification areillustrated in FIG. 3.

With reference to FIG. 3, the combining stage 178 of FIG. 1 is dispensedwith. The RF amplifier to which the modulated power supply stageprovides a power supply voltage is modified, in accordance with knownprinciples, as two-stage parallel RF amplifiers 302 and 304. The two RFamplifiers 302 and 304 are connected to amplify the same input signal online 306, and combine (by means not shown but within the scope of askilled person) their outputs onto an output line 308.

The two identical error corrected switched supply voltages on lines 174and 176 are respectively connected to the power supply terminals of theRF amplifiers 302 and 304. Thus in this second embodiment the correctedsupply voltages from the two correction amplifiers are not combined, butdelivered directly to respective RF amplifiers. In general, n correctedsupply voltages may deliver supply voltages to n parallel RF amplifiers.Further modifications may be possible, e.g. with one or more sub-sets ofthe n corrected supply voltages being combined for delivery to one ofthe plurality of RF amplifiers.

In an arrangement in accordance with the second embodiment as shown inFIG. 3, it is necessary for the individual corrected voltage signalsfrom the n correction amplifiers to be combined in order to provide thesignal for the feedback path to provide the second input to thedifference block 106. Thus there is illustrated in FIG. 3 a voltagecombiner 310 which receives as inputs the corrected voltage signals onlines 174 and 176, and provides a combined signal to the scale block 152(referring to the example of FIG. 1).

In the exemplary arrangement of FIG. 3 the RF amplifiers 302 and 304 arepreferably identical.

A further advantage can be achieved by the arrangement of the secondembodiment as illustrated in FIG. 3. It is desirable for the path lengthbetween the output of the voltage supply modulator and the supply inputto the RF transistors to be as short as possible. By using a distributedcorrection amplifier, as described herein, the path length to the RFamplifier can be kept shorter than if a single high power correctionamplifier were used. This leads to improved high frequency performance.

The reduction in path length can be achieved by controlling where thephysical outputs and physical inputs of the devices are located, forexample, in an arrangement where the modulated power supply and theamplification stage are provided on separate ICs.

The invention has been described herein by way of reference toparticular examples and embodiments, for the purposes of illustratingthe invention and its embodiments. The invention is not limited to thespecifics of any embodiment descried herein. Any feature of anyembodiment may be implemented in combination with features of otherembodiments, no embodiment being exclusive. The scope of the inventionis defined by the appended claims.

What is claimed is:
 1. A power supply stage comprising: a stage forgenerating an intermediate supply signal in dependence on a referencesignal representing a desired power supply; a plurality of correctionamplifiers, each adapted to generate a corrected signal based on anoutput power supply voltage of the power supply stage and wherein thecorrected signal tracks the reference signal; and a combiner forcombining the plurality of generated corrected signals and theintermediate supply signal to provide the output power supply voltagewith higher output current capability.
 2. The power supply stageaccording to claim 1 wherein the combiner is a current combiner.
 3. Thepower supply stage according to claim 1 wherein the output power supplyvoltage is provided as a power supply signal to an RF amplifier.
 4. Thepower supply stage according to claim 1 wherein the stage for generatingthe intermediate supply signal is adapted to select one of a pluralityof power supply voltages in dependence on the reference signal.
 5. Thepower supply stage according to claim 2 further comprising a pluralityof combiners for combining the intermediate supply signal with each ofthe plurality of corrected signals to generate adjusted supply signals.6. The power supply stage according to claim 5 wherein each correctionamplifier receives an input signal representing a difference between thereference signal and a sum of the corrected signals.
 7. The power supplystage according to claim 5 wherein each combiner comprises atransformer.
 8. The power supply stage according to claim 7 wherein theplurality of corrected signals is connected to a tap of a respectiveprimary winding of each transformer, and the intermediate signal isconnected to a tap of a secondary winding of each transformer, and theadjusted supply signals are formed on another tap of the secondarywinding of each transformer.
 9. The power supply stage according toclaim 7, wherein the combiner comprises a connection between taps oftransformers on which the adjusted supply signals are formed.
 10. Thepower supply stage according to claim 1 wherein the intermediate supplysignal is a voltage supply signal.
 11. A method of generating an outputsupply signal comprising: generating an intermediate supply signal independence on a reference signal representing a desired power supply;generating a plurality of correction signals tracking the referencesignal in dependence on the intermediate supply signal and the referencesignal; combining each of the plurality of correction signals with theintermediate supply signal to generate a plurality of adjusted supplysignals; and summing the plurality of adjusted supply signals to providean output power supply voltage to an amplifier.
 12. The method of claim11 further comprising the step of providing the plurality of adjustedsupply signals as power supply signals to a corresponding plurality ofparallel connected amplifiers.
 13. The method of claim 11 wherein thestep of generating an intermediate supply signal comprises selecting oneof a plurality of power supply voltages in dependence on the referencesignal.
 14. The method of claim 11 wherein the correction signalsrepresents an error between the reference signal and the output powersupply voltage, and wherein the method further comprises amplifying thecorrection signals.